1. Field of the Invention
The present invention relates to a suspension system which is suitable for use, for example, in vehicles.
2. Description of the Prior Art
FIGS. 1 and 2 show an air suspension as one example of suspension systems according to the prior art.
In the figures, reference numeral 1 denotes an outer cylinder that constitutes a shock absorber body. An inner cylinder 2 is coaxially provided inside the outer cylinder 1. The upper end of the outer cylinder 1 is closed with a rod guide 3 and a cap 4, and the lower end is closed with a base cap (not shown). A piston rod 5 projects upwardly from the inner cylinder 2 through the rod guide 3 and the cap 4. The lower end of the piston rod 5 is rigidly secured to a piston (not shown) that is slidably fitted in the inner cylinder 2. The projecting end of the piston rod 5 is attached to a mount 17 (described later) through a nut 6, for example, so that the piston rod 5 extends from and withdraws into the outer cylinder 1 in response to vibration of the vehicle.
An upper shell 7, which is in the shape of a tube one end of which is closed, is rigidly secured to the projecting end portion of the piston rod 5 through the nut 6. A lower shell 8 is rigidly secured to the open end of the upper shell 7 by means, for example, of welding. The lower portion of the lower shell 8 is defined as a reduced-diameter portion 8A which extends to the periphery of the shock absorber body. A tubular member 9 is rigidly secured to the outer periphery of the intermediate portion of the outer cylinder 1. A rubber tube 10 has an inner wall and an outer wall, which are connected together at the respective lower ends thereof by a U-shaped portion. The inner and outer walls of the rubber tube 10 are rigidly secured to the upper end portion of the tubular member 9 and the lower end portion of the lower shell 8, respectively, in such a manner that no air will leak through the joints. Thus, an air chamber 11 is defined between the outer cylinder 1 and the projecting end portion of the piston rod 5. Compressed air is externally supplied into and discharged from the air chamber 11 through an air supply and discharge valve 12. Thus, the air chamber 11 functions as an air spring that constantly biases the piston rod 5 in a direction in which it is extended.
A height sensor 13 is secured to the upper shell 7 inside the air chamber 11. The height sensor 13 has a plurality of reed switches (not shown) which are vertically spaced at predetermined intervals. Each reed switch is turned on/off by a magnet 14 that is attached to the upper end portion of the tubular member 9. More specifically, when the upper shell 7 moves up and down relative to the outer cylinder 1, together with the piston rod 5, the height sensor 13 moves relative to the magnet 14, so that the reed switches come close to or away from the magnet 14 to turn on or off, thus sequentially outputting vehicle level detecting signals through a lead wire 15.
A mounting bracket 16 is provided on the lower end of the outer cylinder 1 to secure the outer cylinder 1 to a member that is provided on an axle of the vehicle, for example, a combination of a knuckle bracket 21 and a knuckle spindle 23, which will be described later.
Reference numeral 17 denotes a mount that is provided on the projecting end portion of the piston rod 5. The mount 17 comprises a piston rod-side mounting member 17A that is secured to the projecting end portion of the piston rod 5 through a bearing 18, a vehicle body-side mounting member 17B that is attached through bolts 19 to a member that is provided on the vehicle body, for example, a strut tower 20, described later, and a rubber annular mount member 17C that is rigidly secured to the mounting members 17A and 17B by means, for example, of baking to resiliently support the piston rod 5 with respect to the vehicle body through the mounting members 17A and 17B. The wall thickness of the rubber mount member 17C gradually changes in the circumferential direction to form a thick-walled portion 17C.sub.1 and a thin-walled portion 17C.sub.2, which oppose each other diametrically. The mounting member 17B of the mount 17 has a plurality of bolts 19 which are rigidly secured thereto to secure the mounting member 17B to the strut tower 20 (described later). When the mount 17 is attached in this way, the thick-walled portion 17C.sub.1 of the mount rubber 17C is strongly compressed and elastically deformed, causing a moment to act on the piston rod 5 in the direction of the arrow B.
The bearing 18 has its inner ring rigidly secured to the projecting end portion of the piston rod 5 through the nut 6 and its outer ring rigidly secured to the mounting member 17A of the mount 17 by means, for example, of welding. When the piston rod 5 receives a turning force from the outer cylinder 1 due to the reason described later, the bearing 18 allows the piston rod 5 to rotate relative to the vehicle body. At this time, the mount 17 will not rotate because the mounting member 17A is rigidly secured to the outer ring of the bearing 18 and the mounting member 17B to the vehicle body. However, since the upper and lower shells 7 and 8 are secured to the inner ring, together with the piston rod 5, the shells 7 and 8 rotate relative to the vehicle body, together with the piston rod 5, and they can follow the rotation of the outer cylinder 1, together with the tubular member 9 and the rubber tube 10.
Reference numeral 20 denotes a strut tower that constitutes a part of the vehicle body at a position which is closer to a front wheel of the vehicle. To the strut tower 20 is attached the projecting end of the piston rod 5 through the mount 17. Reference numeral 21 denotes a knuckle bracket on the axle, to which the mounting bracket 16 is attached through bolts 22. A knuckle spindle 23 is provided on the knuckle bracket 21 as an integral part thereof, and a front wheel 24 of the vehicle is rotatably attached to the knuckle spindle 23. The front wheel 24 is connected to a steering wheel (not shown) of the vehicle through a lever 25 that is integrally provided on the knuckle bracket 21, so that the front wheel 24 can be steered by the steering wheel.
When the suspension system of the prior art, having the above-described arrangement, is used for supporting a front wheel of a vehicle, as shown in FIG. 2, the mounting bracket 16 is secured to the knuckle bracket 21 for the front wheel through the bolts 22, and the mount 17 is secured to the strut tower 20 of the vehicle body above the front wheel through the bolts 19. At this time, the thick-walled portion 17C.sub.1 of the mount rubber 17C of the mount 17 is compressed by externally applying a load thereto so that it is deformed from the shape that is shown in FIG. 1 into the shape shown in FIG. 2. As a result, the thickness of the thick-walled portion 17C.sub.1 becomes substantially the same as that of the thin-walled portion 17C.sub.2. Then, compressed air is supplied into the air chamber 11 according to the vehicle level detecting signal from the height sensor 13, thereby adjusting the level of the vehicle and constantly biasing the piston rod 5 in a direction in which it is extended, and thus supporting the vehicle body on the axle through the suspension system.
When vibration is applied to the vehicle when running on a rough road, the piston rod 5 extends and contracts. In consequence, the piston slides inside the inner cylinder 2, thereby generating a damping force by the action of oil in the inner and outer cylinders 2 and 3, and thus absorbing the vibration. On the other hand, when a turning force is applied to the outer cylinder 1 through the mounting bracket 16 by steering the front wheel, since both the piston rod 5 and the upper shell 7 are rotatable relative to the vehicle body by means of the bearing 18, as described above, the piston rod 5, the upper shell 7 and the rubber tube 10 rotate together with the outer cylinder 1, thereby preventing the application of a torsional load to the rubber tube 10.
Since the outer cylinder 1 is attached to the front wheel of the vehicle through the mounting bracket 16, the outer cylinder 1 is subjected to a moment in the direction of the arrow A by the tire reaction of the front wheel, and this moment would tend to cause the piston rod 5 and the outer cylinder 1 to locally push each other extremely strongly through the rod guide 3, so that abnormal friction would likely occur between the rod guide 3 and the piston rod 5.
However, since the projecting end portion of the piston rod 5 is attached to the vehicle body through the mount 17, and the thick-walled portion 17C.sub.1 of the rubber mount member 17C of the mount 17 is attached to the vehicle body in an elastically compressed state, as shown in FIG. 2, a moment in the direction of the arrow B can be applied to the upper end portion of the shock absorber body, for example, the piston rod 5, by the elastically deformed rubber mount member 17C, so that the moment in the direction of the arrow A that is generated by the above-described tire reaction can be canceled by the moment in the direction of the arrow B, thus preventing the occurrence of abnormal friction between the piston rod 5 and the rod guide 3.
The above-described prior art suffers, however, from the problems that, when the suspension system is to be attached to a vehicle, the rubber mount member 17C of the mount 17 must be compressed by externally applying a load thereto so that the thickness of the thick-walled portion 17C.sub.1 becomes substantially the same as that of the thin-walled portion 17C.sub.2, and the mounting operation, which is conducted with the rubber mount member 17C being compressed, is therefore extremely difficult and hence extra time and labor are consumed in mounting the suspension system onto the vehicle.